It is known that object-oriented software applications, such as those using Java™, C++ and C# or other object-oriented programming languages, consist of classes, each which contain methods, also known as functional members, or functions, that contain the instructions to run an application as well as data members or fields. Classes are “instantiated” in order to create objects. Each object contains its own set of data as specified by the data members of the class, and the functional members of any given object are capable of acting on the data members of the object. Objects can be passed into a method invocation in a variety of ways. In Java™, for example, object entries can be accomplished in the following ways: as method arguments or method signature parameters (including the “this” object as a hidden parameter for a non-static method), as field reads, as reads from array object elements, as objects returned form invoked methods, and as exception objects caught from invoked methods throwing the exception objects. Objects can be created within a method by an object creation instruction. Objects can be passed out of a method invocation in a number of ways; objects that are present during a method invocation are stored on the operand stack (Java™), in registers (non-Java™), and in local variables. The references and pointers to objects may change locations as each instruction is executed within a method.
As the instructions of a method are executed, objects are passed to/from different locations in a number of ways, such as by method invocation (stack, locals, registers), by passing to other method invocations, object fields, array elements, and other elements within the running application.
Determining the possible paths that objects may follow inside a method invocation prior to runtime is often required for various processes within an object-oriented software application, and for various optimizations to the software application. This information can be used for various purposes. One use is to incorporate this information within control flow analysis to determine which elements of a software application are reachable. Eliminating unused elements results in less memory usage on the file system and at runtime, and also provides performance improvements. Another use is to incorporate this information with escape analysis, which determines those objects that remain reachable after a method invocation has completed. Escape analysis allows compilers or virtual machines to remove locks, to make memory use more efficient by allocating objects on the stack (making collection automatic, rather than relying on garbage collection), and to apply other optimizations to an application.